11 replies to this topic

[Deekay]

Want to run a 12v fridge in my truck camper full time while on summer trip. Lets say the fridge draws @ 3 amps an hour. Will be able to keep the solar battery charged while driving and will also use a portable solar panel as well. So my question is how many watt solar generator would be needed.

 

Thanks

[ckent323]

The answer depends on the specific refrigerator (brand and capacity) as well as the operating conditions (temperature, e.g. summer heat). 

However, in general, a 12 volt fridge uses between 30 and 55 Ah (amp hours) per day on average.  Since you did not specify I suggest assuming 55 Ah a day for sizing to be sure you have sufficient capacity plus some margin.

In order to provide more detail and suggestions additional information is needed:

What do you mean by Solar battery?

Do you have a house battery in your camper?  If so what type of battery?

How do you plan to recharge the battery?  Shore power?  Solar Panel?  From your truck?   a combination of these?

What equipment for charging do you have already?  Solar panels?, Truck to camper charging?

How many days will you need to operate the refrigerator before recharging?

What other items will you be operating on 12v?  Ceiling fan?  Lights?, Water pump (if you have a pressurized system)?  radio? TV? Computer and Cell Phone recharging? CPAP? Electric cooktop? Heater fan (at night)?  etc.

Lots to consider if you have not already done so.

 

I hope this is helpful.

 

Crag
 

[TacomaAustin]

Just a newbie comment - Not every day has full, cloudless sun.  So, start with at least 200 watts of photovoltaic cells.

 

Also, what size portable lithium power supply are you planning to use?   1200 watt hours of storage will be more than enough to get you through a day of no solar, if it is only a small chest 12V fridge.   If the ambient temps are not over 100°F, then you'll be good for a couple of days, but just barely - if there is no sun.

[Vic Harder]

+1 to what Craig said.  Good idea to slow down a bit and think about what the power needs are will ensure you build a system that works well the first time.  The 3A draw from the fridge is a good starting point.  That's about what mine uses, and it runs about 40% of the time in 80*F heat.  3A * 24 hours in a day = about 75AH a day, but it is only running 40% of the time, so 75*.4 = 30AH

 

If you are building a LiFePo4 based system, a 100AH battery would be good for 3 days (30AH *3 days = 90AH) without charging and no other loads.  Two days would be easy.  So you are parked in the shade for two hot sunny days, and that you need to recharge fully on day 3.  That means recharging 3 days worth... 90AH on day 3.  That's 10A of charge for 9 hours, or some other combo to get 90AH. 

 

If you have 120W of solar panels, they will give you roughly 10A (more like 8A) in ideal sunny conditions (120W = 12V * 10A).   But will you get 9 hours of sunshine?  Not likely.  So, aim for 2x that, or a 240W solar suitcase.

 

Practically, I would have my solar panels in the sun somehow, so that they are charging at least part of the day, and I don't end up just drawing power but also putting some power back into the batteries.

 

For reference, I have about at 55-65AH daily draw, 200AH of LiFePo4 batteries, and 330W of solar.  That works well for us, unless we are using the Induction cook top a lot, and then I need to drive as well to charge up the batteries.

[Deekay]

Thanks guys for the info- For the seperate 12v fridge  was thinking of using a portable solar generator which can recharge by car charger when driving and also use @ 200w panel solar to charge it as well. The camper does have a fantastic fan which would be used from its house battery and would be used to charge tablet. When camper is plugged in to trailer harness it charges the house battery. It has a dometic 3.7cu  3 way fridge however I dont know how efficent these are when set to 12v to run off solar compared to the newer type dedicated 12v fridge freezer like the Whynter and Iceco types drawing @3amp an hour. Picking up this used truck camper next month so trying to prepare what my options are. Maybe it makes more sense to go with 200ah lifepo4 as the house battery and do 200w hard panels on top instead of the portable solar generator?

[Vic Harder]

3 way fridges are very inefficient on 12VDC... 10A draw is typical, I think.  Use the propane whenever possible.

 

The factory wiring to charge from the truck is almost useless.  

 

I'm biased towards roof mounted PV.  I have a 330W panel on mine, and 200AH of Battle Born LiFePo4 batteries.  Overkill for what you are probably needing.  We run an induction cooktop. Without that, a single 100AH lithium battery is plenty for most folks.

[TacomaAustin]

Maybe it makes more sense to go with 200ah lifepo4 as the house battery and do 200w hard panels on top instead of the portable solar generator?

 

That is a good match for a slide-in camper.  However, and as mentioned by Vic, you will need to run that RV industry fridge on propane.

Edited by TacomaAustin, 13 March 2023 - 04:59 PM.

[ckent323]

I also recommend rooftop solar.  I see a lot of people adding extra panels.  I had 200 W of panels and I found that on successive cloudless days I was running my battery down further than desired.   I created a comparison spreadsheet and discovered that using a single large panel (e.g. 360 w) is cheaper and lighter in weight than any combination of 100 - 200 watt panels.

I bought a high quality LG 360 W panel for $310.   I also upgraded my Victron controller to a 100/30 smart Solar unit.  I already had a Vicron BVM.

We have two Lifeline 6v 220 Ah AGM batteries in the camper providing a usable 100 Ah of power.  They cost $300 each in early 2018 and are still working great with only a few cycles on them.

Our camper has a factory 3-way fridge and it is mostly run on propane.  It cools well on 110V but not well on 12 v.

The solar works so well I have not needed to connect the truck electrical to the camper since installing the new panel.

I have a BlueSea ACR with dash mounted switch installed having 80 amp resettable fuses at the camper and the truck batteries in case I needed to connect the truck to the camper (I have a"dumb" alternator so no DC-DC charger) but I have never needed to use it.

We have a Dometic CFX-35 12 v refrigerator in the cab of our truck behind the center console (extended cab) and it works great for keeping drinks, sandwiches, carrot and celery sticks and such cold.  We shut if off when the truck is not running so we don't risk depleting the starting battery of the truck.

If I were doing it now I would install LiFePO4 instead of AGM house batteries since competition has made LiFePO4 more cost competitive since 2018.  That would necessitate a DC-DC charger if connecting the truck to the camper since the truck has an AGM starting battery.

 

I hope this is helpful

 

Craig

Edited by ckent323, 13 March 2023 - 04:16 PM.

[M1010 Mike]

3 way fridges are designed to run on propane or 110v AC.  They have 12v DC for when you are driving and cannot use propane but you have the engine running so you are charging all the time.  Run off 12v DC, even with solar, you are likely to never get the battery charged.  When I got my FWC, I had one trip with the 3 way.  First mod I did when I got back was to replace it with a dedicated 12v DC compressor fridge.  Never had a problem after that and I didn't have solar.  Just charging from the truck when driving.  When stopped, 100% battery only.  Never once ran out of power.

[Deekay]

I plan on removing 3way and replacing with 12v fridge freezer  or leaving it as storage compartment. So from the advice Im getting use a lifepo04 battery 100ah as my house battery in camper with around 200w to 300w panel this should be sufficent to run 12v fridge full time-